The development and prevalence of the projector greatly facilitate various large and medium meetings or exhibitions. A projector adapted to an individual or meeting of two or three persons, image display for a digital camera, multimedia information display of personal PC and the like needs to be designed lighter and easy to carry, and it also demands that the projector can be quickly turned on and turned off, with lower power consumption, a longer service lifetime, and a relatively low cost. However, the currently widely used projector with a light source of arc lamp has not only high power consumption but also a big volume, which limits its application in the field of projection for personal use.
With the development of the laser technology and miniaturization of the laser device, the laser projection devices are used more and more widely. The phosphor wheels and the dichroic mirrors are often used in the light source for a laser projection device for treating light from a light-emitting unit so as to emit beams of light having ideal wavelengths, for instance, beams with red, green, and blue light. However, the light blocked by the dichroic mirrors is not fully used such that the optical efficiency of a light engine is low. Besides, to enable a light source to generate one beam or beams of light with three colors, i.e., red, green, and blue colors, the existing laser projection device, in which the light source structure used is complex, needs at least four dichroic mirrors in order to, for example, generate a beam of light with three colors, therefore, it has a light engine with a relative big volume such that the laser projection device also has a big volume.